


Hello Darkness My Old Friend

by CheetahLeopard2



Category: Assassination Classroom, 文豪ストレイドッグス | Bungou Stray Dogs
Genre: Crossover, Gen, Why Did I Write This?
Language: English
Status: In-Progress
Published: 2020-06-30
Updated: 2020-06-30
Packaged: 2021-03-05 00:41:50
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 4
Words: 4,468
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/25005592
Author URL: https://archiveofourown.org/users/CheetahLeopard2/pseuds/CheetahLeopard2
Summary: IN which Chuuya is hit by an ability that sends him to a different reality (AKA Chuuya joins 3-E)
Comments: 27
Kudos: 192
Collections: Time Travel and World Travel





	1. Chapter 1

**Author's Note:**

> I have really no idea  
>  The title is my mood writing this

Chuuya accidentally lets the ability-user’s hand land on his shoulder- nothing more than a brief tap- and there’s a bright flash of light.

When Chuuya opens his eyes, it’s as though he’d just blinked. He’s in a classroom, students who look about 15 chattering around him.

Frowning, he checks himself. He is _also_ around 15, a bit older, judging by the length of his hair.

With a sigh, he quickly catalogs everything he knows about the ability used on him.

The ability to send whoever was touched into a different reality. They couldn’t alter memories or consciousness or abilities, but could change physical age of whoever was sent into the different reality to suit the reality.

Chuuya’s not unconscious back in his reality- he’s gone. Everything he is is completely trapped in this reality.

Moreover, as far as he can tell, no one in this reality has an ability.

He stops his introspection as a stern-looking man walks in, followed by a very tall yellow… _thing_. Luckily for Chuuya, he’s not the only one who looks surprised, so this can’t be a common occurrence.

The stern-man, introduced as Karasuma, begins to explain. Using Karasuma’s explanation, Chuuya pieces together facts about the reality.

It’s the same as his- aside from the lack of abilities- except the moon’s been blown up. Apparently by this creature, who they’re supposed to learn to assassinate, who’ll blow up the earth next year otherwie.

Chuuya doesn’t have much of an interest in killing without a reason in a reality where he doesn’t have to- even if he’s being given a free, legal pass.

If he’s here for long enough that the Octopus thing blowing up the earth becomes his concern, he’ll kill him. But otherwise…

Chuuya looks around him, at the wooden desks and the chalkboard and the kids freaking out, and thinks that maybe it would be nice to have a bit of a childhood for a while.

He accepts the handgun, rifle, and green training knife he’s given with a nod.

The guns aren’t a make he’s seen before, and up front Karasuma explains that they’re BB guns with anti-creature material.

Curious, Chuuya disassembles it on his desk, taking note of the ammo chamber being built differently than one in his reality that shoots real bullets.

The kid next to him, who looks like a bit of a brute with the top of his hair brown and the underneath bleach-blonde, is looking at him with a furrow in his brow, and Chuuya quickly reassembles the BB gun and looks up as Karasuma continues talking.

He reads through and signs the Non-Disclosure Agreement, which honestly is like a contract Mori-sensei would write up for a business deal except with far more loopholes, and then the day is over.

Chuuya lingers in his seat after dismissal, mostly because he doesn’t know where he’s supposed to be in this reality.

Luckily, or perhaps unluckily, so do most of the other students.

“So who’re you?” a girl with long blonde hair and a teasing smirk asks Chuuya from a couple seats ahead, and he spins the idea of telling the truth around in his mind. There’s not any harm in it, so he shrugs.

“Nakahara,” he offers, “And you?”

“Nakamura Rio, call me Rio” she replies, taking his response as an invitation to take a seat in the empty desk to his left, “What’d you do to get sent down to class 3-E?”

It takes all of two seconds for Chuuya to realize she’s talking about a ranked class system, which Ane-san had thankfully taught him about. E must be a low class in this system.

He shrugs again, “pissed off the wrong person.”

She laughs, “Fair enough.”

The girl who’s pink-blonde and sits in the front walks back to join their conversation, “Did you just transfer to Kunugigaoka?”

“Yeah,” Chuuya answers, which isn’t really a lie, “Can you give me some advice as to how this place operates?”

“Oh, for sure! I’m Kurahashi Hinano, call me Kurahashi. So I’m sure you’ve noticed how we’re on separate from the main campus-”

Chuuya did not notice, but nods regardless.

“- that’s because we’re the ‘End Class’ and everyone hates us because they’re told they don’t want to end up like us. We’re on a bit of a later start and end because of the trek up the mountain-”

She keeps explaining, and Chuuya nods along, making mental notes the whole while.

They strike up a pleasant-enough conversation, which continues when they walk down the mountain together. Kurahashi and Rio both go left at the end of the path, so Chuuya lies and says he has to go right.

Inevitably, he ends up sleeping on the mountain. It reminds him of his days back with the sheep.

The next couple of days go similarly, the only hitch being when a blue-haired boy who goes by Nagisa very nearly suicide-bombs Koro-sensei, and he threatens everyone’s families.

Koro-sensei holds him back that class, inquiring about his living situation, how he hadn’t found a Nakahara house plate.

Chuuya shrugs, “I’ve been sleeping in a cave.”

Koro-sensei freaks out for a bit, until he finally says that Chuuya’s welcome to stay in the school building at night.

* * *

This Karma kid looks like he might be trouble. He’s skilled enough with a knife, although it’s clear he’s lacking in experience against equally matched opponents.

It’s rather funny to watch him get more and more worked up as Koro-sensei pampers him and doesn’t die, and at the end of the day Chuuya joins Nagisa in following him to the cliff.

Karma starts talking about how he’s always wanted to kill a teacher, and Chuuya wants to laugh, to warn the kid that killing isn’t something to be taken lightly, that he’ll be haunted by every soul he takes. The legions in Chuuya’s nightmares have quieted over time, but this boy has a choice.

And then Karma does what is possibly the most annoying this he could’ve done. He stands and turns, gun pointed at them, before falling backwards.

Nagisa runs to the edge with Koro-sensei, and Chuuya follows.

“Great,” Chuuya sighs, “another suicidal maniac.” And then he turns to Koro-sensei, who looks more stricken than anything else, namely ready to save Karma.

“I guess I’ll handle it then.”

And he leaps, ignoring Nagisa screaming behind him and destroying the tentacle that tries to pull him back with barely a wave. He angles himself down headfirst, and scowls, flips, and slows his speed when he reaches Karma, who looks shocked and more than a little annoyed.

“You’re not Koro-sensei.”

“And you’re not gonna die,” Chuuya returns evenly as he begins adjusting Karma’s gravity so he’ll slow to a stop without a dangerous jolt, guiding them towards the cliff wall so he doesn’t have to explain himself beyond ‘oh I grabbed Karma and the cliff wall and we skidded down.’

“You jumped with me,” Karma says, closing his eyes peacefully, “so I suppose we both will.”

Chuuya rolls his eyes, “Dramatic fuck,” he mutters before looping an arm around Karma’s waist and grabbing the cliff wall as the come to a stop.

Koro-sensei is there in an instant, exclaiming that even though he’d set up a fall-breaking web at their projected landing spot that was still much too dangerous and now he has to help them down and-

Chuuya rolls his eyes again, making sure Karma’s steady before turning and starting to scale the cliff wall, ignoring Koro-sensei’s fussing.

As soon as he’s far enough up and to the side, he pushes off the wall and flies up the rest of the way, to where, of course, they’re already standing.

Karma says something about treating them to dinner, Koro-sensei squawks about Karma stealing his wallet, and then- curiously, Karma turns to Chuuya, “I hear you’re staying on-campus overnight.”

“I am,” Chuuya confirms, a bit weary of where this conversation might be headed.

“You can come live with me if you want, as a thanks for saving my life.” Karma almost looks embarrassed.

“Thanks, kid. That’d be great.”

Karma’s expression sours a bit, “Only if you don’t call me kid.”

“Alright,” Chuuya hold out a hand, and Karma shakes it.


	2. Chapter 2

**Summary for the Chapter:**

> I mean I guess

Chuuya walks home with Karma after that, they ended up not getting dinner on account of Koro-sensei being too broke.

Karma lives in a very large house, with a gate and a garden that reminds Chuuya a bit of Kouyou. The reminder brings a bittersweet smile. He has no way to get home until the people there get the ability-user to tell them how to bring him home.

Karma’s mostly silent as they approach the house, until he freezes at the doorway.

“Shit,” he curses, and Chuuya follows his gaze to an ostentatious car in the driveway, “My parents are home.”

“Parents?” Chuuya can’t help but say, surprised. He really shouldn’t be so surprised, this is a regular private school setting, of _course_ the students are going to have parents. But back home, Chuuya can’t think of anyone he knows who has parents, aside from vaguely being aware some people in the Guild have them.

Luckily Karma takes his question differently than Chuuya meant it, and starts explaining his home life.

“They could hardly be called parents, with how often they’re around,” he laughs, a bit bitterly, “I’m really surprised they’re here.”

“I’ve never met anyone’s parents,” Chuuya admits, “How should I act around them?”

Karma gives him a deep, searching look, but Chuuya’s used to Dazai and ensures his posture and expression betray nothing.

“Honestly, just act surprised I have any, and say anything you can to annoy them. I’ll tell them you’re only here for the night to work on a project so they can’t reasonably stop you from staying here,” Karma smirks a bit, “Just piss them off.”

Chuuya laughs, and Karma opens the front door. Karma doesn’t bother taking off his shoes in the entryway, so Chuuya follows his example, scowling a it when he recognizes how expensive the rug they’re walking on is.

Karma’s parents are in the kitchen, and Chuuya keeps his head held high as they walk in.

His father has dark hair slicked back, and his mother has bright red hair and looks decidedly foreign.

What concerns Chuuya is the insignia on the papers Karma’s parents are looking over. It looks remarkably similar to the one used by one of the Port Mafia’s controlled companies, one that manufactured weapons in France if Chuuya remembers correctly.

“Karma,” Mrs Akabane says amicably, before continuing in French in the same tone, “who the fuck is this?”

If Chuuya weren’t trained to gather information before playing all his cards, he would laugh.

As it is, he frowns a bit and looks confused, going to stand by Karma’s father.

“Hello, sir. I’m Nakahara, Karma’s classmate,” he hold his hand out for a handshake, which Mr Akabane wipes his hands after, saying nothing before he goes to stand by his wife to question Karma.

Keeping one ear on the conversation, he gives the forms a quick and subtle once-over. Yep, weapons trading, but still with no mentions of ability users, and without any of Mori’s aliases (that he recognizes) anywhere.

The document is in carefully worded English, and certainly outlines some less-than-savory connections Karma’s parents have with assassins and organized crime. Interesting.

He maintains a careful distance from the table and plays the part of an awkward, normal 15 year old, shifting from foot to foot and looking around at everything.

“Why would you let a stranger into our house?” Mr Akabane was asking, also in french.

“He’s not a stranger,” Karma answers fluently, standing tall, “he’s a friend, from school. We’re doing a project and he’s just staying tonight.”

“From your class? After your suspension? You expect us to believe that?” Mr Akabane questions, his tone and expression contrasting his words greatly.

“He’s 15,” Karma says flatly.

“You know our work! If he finds out anything, at all, he’ll be killed. How could you risk one of your friends?” Mrs Akabane takes a different approach.

“How could you risk me, with that logic?” Karma asks, and Chuuya has to bite the inside of his lip to keep from laughing. This kid really is a bit like Dazai.

“You’re going into the organization someday,” Mrs Akabane says ominously, “just hope that day isn’t soon.”

Karma stiffens minutely, and Chuuya takes that as his cue to interject. While it would be fun to surprise them with fluent french, or pretend he only knows minimal french for their reactions, it’s probably not the smartest move.

Although… they are pissing him off. Karma’s life hasn’t been fucked up in the way Chuuya’s has- he should have the choice not to join whatever organization replaces the port mafia here.

He makes his choice.

“Karma, you have yet to have killed someone, correct?” Chuuya asks, in Japanese.

His parents turn to him in eerie silence and unison.

“So how’re we supposed to plan the assassination of the character we were assigned? It’s a rather odd project,” he continues on, pretending to be oblivious to the way the elder Akabanes deflate in relief.

Karma forces a laugh, though is glaring daggers, “You say that like you _have.”_

It’s meant to be a joke, Chuuya can tell. But he also knows he has the eyes of a murderer and blood that stains further than simply his hands, and so he smirks a bit and simply shrugs, “I just think it’s an odd choice for a book project.”

“Yeah, I guess,” Karma says, and his parents exchange a look.

“Let’s have dinner,” Mrs Akabane suggests, and Karma nods.

“I’ll go cook something-”

“Let’s go out,” Mr Akabane says, surprising all of them.


	3. Chapter 3

They take them to an upscale french restaurant, in a fairly obvious ploy to see if Chuuya can speak french.

Chuuya sits with Mrs Akabane on one side of the booth, Karma and his father on the other. Chuuya and Karma are essentially trapped.

Chuuya leans over to Karma once they’re settled with menus, “What would you recommend?” he asks, with the voice of a teenager who doesn’t want to admit he doesn’t understand the menu.

Karma looks at him suspiciously, “I’ll order for you, if you want.”

“Alright,” Chuuya answers.

“Any allergies we should know of, if Karma’s ordering for you?” Mrs Akabane asks, and Chuuya can’t tell if she’s genuinely concerned or not, but shakes his head regardless.

A waiter comes by, and Karma keeps his word and orders for him, pointing to it on Chuuya’s menu so Chuuya can figure it out. Seems like they’re both eating steak- the most expensive thing on the menu.

Hilarious- for the only person Chuuya knows to have any, Karma really hates his parents.

While they wait, Mrs Akabane picks up the wine menu, which she allows Chuuya to look over with the amused expression adults always seem to have towards kids who ask like adults.

Of course, in his reality Chuuya’s 23, but she doesn’t know that.

He scans the wine menu quickly, frowning at the fact that he wouldn’t be allowed to drink any even as his body is the physical age he was when Kouyou found his wine tasting skill passable.

Nonetheless, he magnanimously points out one of the wines and says, “I know this is good, my Ane-san would drink it when she could.”

Which… isn’t technically a lie.

Mrs Akabane looks surprised, then smooths out her expression, “I don’t drink red wine often.”

Chuuya nods in mock-understanding, “Alright, it’s rather smooth and has an open flavor. According to my Ane-san.”

“It couldn’t hurt to try,” Mr Akabane shrugs, and Chuuya smiles in return. His heart pangs a bit with the realization he might never drink with Kouyou again, but waves off the feeling.

Karma has all the subtlety of the average 15 year old, and asks, “Why the past tense?”

“She’s missing from this world,” Chuuya says carefully, again not a lie, and sounding haughty enough that a hurt 15 year old trying to reconcile death would say it.

“I’m sorry for your loss,” Mrs Akabane says gently, staring daggers at her son.

Chuuya shrugs, “It’s alright, I’ve got good friends like your son to help me through it.”

Karma send him a grateful look, and Chuuya nods at him.

The food arrives, and Chuuya again sends his thanks to Kouyou’s teaching, this time for knowing which fork to use.

There’s a bit of polite conversation before Chuuya decides to have some fun.

“So Mrs. Akabane, what do you do for work?”

“I’m co-CEO of a company with my husband, actually,” she says, nodding to Mr Akabane.

“Ohh,” Chuuya forces his eyes wide and leans forward in false interest, “What company?”

“I doubt you’ve heard of it,” Mr Akabane says flippantly, but answers with the name of the weapons company regardless.

Chuuya forces a blank look on his face, and Mrs Akabane laughs a bit, “It’s alright you haven’t heard of it, our main headquarters runs out in Yokohama.”

“How’s the city doing?” Chuuya can’t help but ask, “I haven’t seen it since I left.”

“Yokohama?” Mr Akabane asks, in a carefully neutral tone.

Chuuya nods, wondering if this may have been a bad idea.

“The city’s doing well, although there might be a bit of conflict coming up last I heard.” Mr Akabane leans forward, “between Ability users.”

Chuuya keeps his voice surprised, “Ability users aren’t real.”

Mr Akabane leans backwards in disappointment, “Hm.”

Karma’s frowning, looking between them before he interjects in french, “Could you not go on about that, father?”

Mr Akabane smirks, but says nothing.

Thankfully, the wine arrives soon after. Unfortunately, Chuuya knows better than to drink any.

They arrive home soon after, and Karma and Chuuya retreat to Karma’s room with a futon.

His parents are gone in the morning.

* * *

Bitch-sensei reminds Chuuya of himself, a bit. Not in her… methods… but in the fact that she’s grown up too fast and seen too much death and torture in her short 20 years. She _also_ never got a childhood, never knew who she really was born as, and knows many languages not out of interest but necessity.

She walks in to her first full class of genuine language-teaching, and Nakahara has to admit that while her sample sentences could use a bit of innocence she’s a decent language teacher.

As everyone’s dismissed for lunch, she calls for him to stay back.

“I don’t know much about being a teacher, or kids,” she admits to him, “but I know the eyes of someone who’s grown up too fast.”

“I don’t doubt that, Bitch-sensei,” Chuuya replies, “You’re 20 and have seen and caused nearly as much death,” he bites down the urge to say ‘ _As I had at 17’, “_ as a small army.”

Irina pauses, considering, “You know too much for a 15 year old.”

Chuuya snorts, “Is that all?”

Irina sighs and sends him on his way.

After lunch is gym. Their first hand-to-hand sparring lesson.

Chuuya considers, weighing his options. He’s missed sparring, and sans his ability, Karasuma might almost be an even match. _Besides,_ he admits to himself, _it might be fun to show off a bit_.

And so, when Karasuma notes that they have an odd number of students, Chuuya raises his hand, “I’d like to fight you, sensei. That fixes it.”

Karasuma nods, and the class breaks into pairs.

Karasuma settles into a starting stance, “Alright, I’ll go easy.”

“Don’t,” Chuuya smirks, before spinning into a high kick.

Before long, Karasuma is fighting in earnest, and Chuuya has him on the defensive.

Other students have paused to make a ring around them. Chuuya’s got around 2 decades worth of life-or-death fighting experience under his belt, and Karasuma has a standard military style of sparring that’s easy enough to predict. Honestly, it’s not much of a challenging fight, but Chuuya’s having fun and downplaying his skill isn’t that hard.

Finally, Karasuma surrenders with a frown, and the other students all start talking at once.

Chuuya ignores them, instead bowing to Karasuma as he would at the end of a spar with Ryuunosuke, the sequence of a winner of a traditional spar to an outclassed opponent.

Irina, who’d apparently been watching the show, sits up straighter at his traditional bow sequence, before setting down he drink and striding purposefully to his side, “Nakahara-kun, how do you know that bow?”

“What do you mean?” Chuuya asks, putting up a mask of innocence, “Does it have some significance here?”

Irina looks him over, and shakes her head, “It’s an old form, I’m surprised is all.”

“I had a traditional trainer,” Chuuya says pleasantly, and the matter is dropped.


	4. Chapter 4

There’s a huge box in the classroom today.

Chuuya doesn’t really know what to make of it, so he takes his seat and waits for Karasuma to explain.

At the words “Autonomous Intelligence Fixed Artillery” Chuuya straightens in his seat. He remembers Dazai explaining to him what an AI is, and this could prove interesting.

At least, he thinks so until it starts shooting everything during class.

Everyone is shouting to have someone shut it off, so Chuuya thinks he’s completely justified when he stands up and stalks over to the AI, fully intent on kicking it until it shuts off.

The AI doesn’t agree. “Threat approaching” it says, which is true, and turns a gun on him.

“Shut up,” Chuuya growls, stepping forward again, so the gun is pressed to his forehead, and the class goes deadly silent.

So, coincidentally, does the AI. Of course, that’s because Chuuya just forced all the wiring inside to collapse in on itself, but the class doesn’t know that.

“Thought so,” he nods.

Chuuya turns to step back to his seat, only to see every eye in the room on him. Koro-sensei, especially.

There’s a moment of silence, before the AI starts smoking.

“Shit’s gonna blow,” Chuuya shouts, and everyone quickly ducks for cover.

That’s pretty much the end of it, or so Chuuya thought.

It’s back again the next day, and before Chuuya can destroy it again Koro-sensei steps in his way.

“No need to worry about it today,” he says, tentacles waving and a smug expression on his face, “I’ve managed to give it sentience!”

Chuuya stares, blinks, turns to the AI and back, and blinks again before deciding, _Eh, stranger things have happened_ , and shrugging.

The class names her Ritsu, and Chuuya could _really_ use a drink.

* * *

It’s just him, Karma, and Irina in the classroom, conversing quietly in English when they hear static.

Chuuya’s the first to stand and face Ritsu, and the static continues a moment more before-

“Nakahara-san!” it’s Atsushi’s face who fills the screen first, then Katai’s, “Are you there?”

“I’m here, Nakajima.” Chuuya ignores the relief at seeing people from his reality, maybe there’s even a spark of hope, “Report.”

Atsushi’s knocked to the side by Ryuunosuke, who’s looking around at Chuuya’s surrounds with interest as he explains, “Captured. The only ways to get you back are to get them to do it- unreliable. Or somehow get Dazai to you and make contact.”

Chuuya exhales slowly, “Right. Were they rogue or-”

“Excuse me,” Irina interjects, “What the fuck?”

And that’s when Dazai’s voice cuts in, “Did you find him?” and then he’s there- on the other side of a screen in a different reality.

“Hatrack, why are you 15 again?”

“Again?” Irina asks, a bit less kindly, and Dazai’s eyes focus on her with a familiar glint.

“I’m 23. And NO, she won’t,” Chuuya interrupts before Dazai can ask, “There seems to be an equivalent to the PM in this Yokohama. Abilities are less well known and less common here, so be discreet.”

Dazai looks. Well, he looks like shit, bags under his eyes prominent, bandages loose. He looks serious when he agrees.

Irina pulls a gun on the device, a real one, and Chuuya sighs, “Irina that is very ill advised.”

Dazai has the gal to laugh.

Karma, who’s been suspiciously silent, speaks then, “Abilities? Like my dad’s on about.”

“Who’s the kid?” Dazai asks.

“A classmate,” Chuuya says, “his parents head the alt mafia here, I believe.”

Karma’s sharp intake of breath confirms it.

Dazai looks marginally more interested, “He have an ability?”

“Yes,” Karma admits, and Chuuya turns in surprise.

“And you haven’t killed Koro-sensei yet?”

Karma shrugs as different sounds of confusion come from the other reality, “Why haven’t _you?”_

Chuuya shrugs right back, “I’m taking a break from carnage.”

Irina turns her gun on Chuuya, “Tell me what the fuck is going on.”

“Uh, Nakahara-san? We have to go, we’ll send Dazai when we can.”

“Alright,” Chuuya nods, “Until then.” The screen blinks back to Ritsu, who looks a bit dazed.

Irina still has her gun trained on Chuuya, and Karma looks uneasily between them.

A minute passes, and Chuuya sighs, “Just shoot at me already, Bitch-sensei. I promise I won’t hurt you.”

“Just explain,” Irina levels back, “and I wont hurt _you_.”

“I’m from a different reality where I’m a head executive of the Port Mafia at 22 and everyone’s trying to figure out how to bring me back,” Chuuya says, rolling his eyes, “Your turn.”

“Wait,” Karma says, bringing a hand to Chuuya’s arm.

There’s a flash, like the one when Chuuya was transferred, and suddenly he’s physically 23 again, in his Mafia attire.

“Huh,” he says, as Karma steps back with his face set in an unusually serious expression.

Irina sniffs, “That doesn’t make much sense, but okay.” She appraises him, “Not bad looking, either.”

“I sure hope not,” Chuuya mutters, checking to be sure- yep, he’s dressed how he was before the reality switch. He has his real gun, real knife, but no hat and no coat, oh well.

“How will we explain this to the class?” is Irina’s first question.

“Indeed,” comes Dazai’s voice, “That should be our second concern.”

They whirl to see him standing behind Karma, “But first should be _how I got here and why I can’t get back_.”

“Mackerel,” Chuuya greets, then, “what the fuck do you mean you _can’t get back_?”

Dazai gives him a flat stare, and Chuuya throws his hands in the air, “I’m gonna go punch something before I kill you, see you chucklefucks in a minute.”

Before anyone can stop him, he’s out of the building.

And then faced by his classmates (?), who take 3 seconds to look at his different clothes, the real gun and real knife in his belt, and flip their shit.

“For fucks sake, slug, you should be smarter than this!” Dazai calls from where they’ve opened the classroom window and Chuuya flips him off without looking.


End file.
